Electricity storage technologies are important technologies for efficiently maximizing performance in areas such as efficient use of electricity, improvement of ability or reliability of a power supply system, expansion of introducing renewable energy in which a range of changes depending on time is large, energy recuperation of a moving object, and the like, throughout an entire energy industry, and their development possibilities to meet demands for social contribution are being gradually increased.
In order to adjust a supply-demand balance of a semi-autonomous local power supply system such as a microgrid, appropriately distribute non-uniform output of development of the renewable energy such as wind power or solar energy generation, and control an influence of voltage and frequency changes generated by a difference from a conventional electric power system, studies on secondary batteries are being actively conducted, and expectations with respect to the utilization of the secondary batteries are being increased in these fields.
Referring to characteristics required for a secondary battery to be used for storing of high-capacity power, the secondary battery should have a high energy storage density, and thus a redox flow secondary battery is being spotlighted as the secondary battery having a high capacity and high efficiency, which is the most appropriate to these characteristics.
The redox flow secondary battery is formed so that a cell frame forms an outline of an entire cell, a center of the cell is divided by an ion exchange layer, and an anode and a cathode are located at both sides of the ion exchange layer.
Further, the redox flow secondary battery is formed to include a bipolar plate and a current collector for externally conducting electricity from each of the electrodes provided, an anode tank and a cathode tank, which store electrolytes, an inlet in which the electrolytes flow in, and an outlet in which the electrolytes flow out.
Various studies are being conducted on such the redox flow secondary battery to develop to an increase in both output and energy efficiency. Recently, a non-aqueous electrolyte rather than an aqueous electrolyte has been mainly used.
As described above, in order to develop the redox flow secondary battery to which the non-aqueous electrolyte is applied, use of the electrode in which affinity with the non-aqueous electrolyte is high and having excellent electrical conductivity is required, and thus research and development of the electrode in which these requirements are satisfied are urgently needed.
In the case of a carbon-based material used for an energy electrode material of a commercial redox flow secondary battery, since affinity with the non-aqueous electrolyte is very low as well as conductivity is significantly reduced compared to a metal electrode, improvement in energy efficiency is limited when applied to a non-aqueous redox flow secondary battery.
Various studies for development of the metal electrodes are being conducted to improve an electrochemical characteristic of the non-aqueous redox flow secondary battery. However, there is a limit on increase of a specific surface area of the metal electrode in a manufacturing process, and thus these studies are not proposing a fundamental solution to an improvement of energy efficiency of the non-aqueous redox flow secondary battery.